1. Field of the Invention
This invention relates to collagen-thrombin compositions, and more particularly to collagen-thrombin compositions which are storage stable.
2. Description of the Prior Art
"Natural insoluble collagen" as used herein means and refers to collagen which cannot be dissolved in an aqueous alkaline or in any inorganic salt solution without chemical modification, and includes hides, splits and other mammalian or reptilian coverings. More particularly, natural insoluble collagen means and refers to the corium which is the intermediate layer of a bovine hide between the grain and the flesh sides.
In young animals there is little intermolecular and interfibrillar crosslinking which provides for some degree of solubility of the collagen.
"Native collagen" as used herein means and refers to collagen, whether natural insoluble collagen or soluble collagen, wherein the quaternary structure of the protein has been preserved.
Collagen constitutes the connective tissue and is the major type of fibrous protein in higher vertebrae. Collagen in its natural state exists in a triple chain helix along with a constant periodicity between aligned triple chains. The triple helical configuration of collagen is sometimes referred to as a fibril and the fibrils align with an axial periodicity of about 640 .ANG..
Although there are several types of collagen, the major type is referred to as "type I" which is the major collagen of skin, bones and tendons. The type I collagen has a chain composition of [.alpha.1(I).sub.2 .alpha.2]. The .alpha.1(I) and .alpha.2 chains are homologous.
The use of collagen in substantially pure form has been proposed for many uses, including burn dressings, as disclosed in U.S. Pat. Nos. 3,939,831 and 3,514,518, and similar medical applications are disclosed in U.S. Pat. Nos. 3,157,524 and 3,628,974.
Among the many uses of collagen which have been proposed in the prior art is its use as a hemostat. Collagen has been known to promote the coagulation of blood along with a healing promotion. One of the advantages of collagen when used as a hemostat or implantation into the body is that the collagen dissolves due to enzymatic digestion and other biological processes. This is due primarily to the nativity of the collagen, and thus, when collagen is to be implanted in the body, it is desired that it maintain its nativity.
Further, it has been recognized that local stoppage of bleeding and tissue bonding can be achieved with blood clotting factors such as thrombin. Several compositions which include thrombin as a blood coagulant have been proposed, such as are disclosed in U.S. Pat. Nos. 2,433,299 and 4,363,319. It is recognized that thrombin in dry form is storage stable when supplied in sealed containers. In order to utilize such thrombin it must be removed from the container and used immediately. Thrombin, per se, had limited use as a blood coagulant because of problems with handling and stability. In its most desirable form, thrombin is incorporated into a pad or substrate of some kind so that it can be applied to the wound. Many attempts, both successful and unsuccessful, have been made in order to provide a storage stable thrombin pad or substrate for utilization in external coagulation areas. With respect to implantable materials, the combination of collagen and thrombin would appear to be ideal for the healing of internal wounds, particularly useful during surgery and the like. The collagen can be utilized as a carrier for the thrombin, and collagen pads or the like with the thrombin impregnated herein can be applied to the wound to promote coagulation with the subsequent digestion of the collagen in the biological system.
For the most part, these efforts have been limited to incorporating stabilized thrombin solutions of unstabilized thrombin solutions into collagen fabrics, pads or the like. However, these thrombin-containing substrates must be used immediately since storage stability has presented a problem. Further, in the thrombin-impregnated collagen substrate the thrombin is mobile so there is a potential for seepage of the thrombin into a particular organ when the impregnated pad is utilized in surgery. Exemplary of collagen-thrombin combinations are those compositions disclosed in South African Application No. 820123 entitled "Material for Sealing and Healing of Wounds." Thus, it has been desired by those workers in the art to provide a thrombin-impregnated collagen substrate wherein the thrombin is immobile and is not capable of migration into a particular organ, and further, where such composition is storage stable.